The ideal amount of light for exposing a frame of film is determined by the speed, or ISO number, of the film. The camera (or photographer) determines from the ISO number of the film and from the brightness of the scene about to be photographed how much of the scene illumination to admit through the camera shutter to the film to create the nominal exposure value corresponding to the film ISO number. Either the aperture size or the shutter exposure time (or both) must be adjusted accordingly. The amount of light is increased by increasing either the exposure time or the aperture size (or both) and is decreased by doing the opposite.
If the camera (or photographer) commits an error in determining the correct shutter exposure time and aperture size used to expose the film frame, the negative image on the color negative film is either slightly washed out (in the case of underexposure) or has insufficient contrast between different objects in the image (in the case of overexposure). The effect is sometimes unavoidable, particularly in cases of high speed photography wherein the shutter exposure time must be extremely short. If the photofinisher is aware of such an error, he can correct such problems by changing the amount of light used to expose the film image onto print paper, in accordance with well-known techniques in the art. The problem is that, absent a skilled photofinishing operator or a sophisticated film image scanner such as those used in the Eastman Kodak Company CLAS 35 film printer, the photofinisher will not necessarily know that a particular film frame has been over- or underexposed.
A more severe problem is that the brightness of the scene may have been so great or so little that the required shutter exposure time and/or aperture size is beyond the range of the camera to provide the correct exposure value on the film. In such a case, the photofinisher does not know if this has happened until after the film has been developed and either an extremely dark or an extremely light image is observed on the film. It would be better if the photofinisher were informed prior to inspection of the film images that a particular frame was beyond the camera's exposure value range.
In the prior art it has been at least suggested that various scene parameters be recorded on film. Specifically, exposure conditions have been suggested as being recorded optically on the film. The disadvantage here is that such information is not available until after the film is developed. Moreover, the information may not be supplemented easily thereafter, since it must be carefully optically recorded on the film using special exposure devices such as those found in some of the higher quality automatic cameras.
While it has been suggested to record various scene parameters such as shutter speed and aperture size adjacent each frame on the film, it has not been suggested how to make such information meaningful to a photofinisher, since such information only has meaning if one knows the brightness of the scene and the capabilities of the camera.
Accordingly, it is an object of the invention to provide meaningful information on film which can be read and supplemented after the film has been taken out of the camera and prior to its being developed. Moreover, it is an object of the invention to provide such information in a manner that automatically correlates information pertaining to a particular film frame with that film frame unambiguously.